Two-way communication system



April 6 1926.

J. c. GABRIEL TWO-WAY COMMUNICATION SYSTEM Filed Feb. 1924 7 [Wm/0r: Job/7C Gabriel by Patented Apr. (5, 152% srrss raster caries.

JOHN G. GABRIEL, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TWOWAY COMMUNICATION SYSTEM.

Application filed February 1, 1924. Serial No. 689,851.

To all whom it may concern:

Be it known that 1, JOHN C. GABRIEL, a subject of the King of Great Britain, residing at New York city, in the county of New 5 York and State of New York, have invented certain new and useful Improvements in Twoay Communication Systems, of which the following is a full, clear, concise, and

. exact description.

This invention relates to two-way con'n'nunication systems.

An object of the invention is to avoid the production of side tone in a receiver ata two-way communication station by energy from the local transmitter.

A further object is to control the responsiveness of the receiver and the operation of the transmitter directly by sound energy without the use of manually operated switches.

ceiver from the local transmitter.

The de velopment of satisfactory means to accon1- plish this result has been attended by certain difficulties which are peculiar to high frequency, and especially to radio, systems. For example, distributed and certain other forms of casual and unavoidable capacity, are substantially non-eifective as impedance elements except at relatively high frequencies. In radio systems, the relatively great difi erence between the energies concerned in the transmitting and receiving functions, and the consequent relatively great diiierence in the sensitivity of the respective transmitting and receiving apparatus, makes the presence of side tone currents especially hazardous to the receiving apparatus.

One type of practicable means involves the use of commutating devices to render the transmitting and receiving circuits alternately operative and in which the necessary commutating functions are accomplished by relay actuated switches, the relays them selves being actuated by a portion of the sound or other form of energy used for signal modulation.

In such an arrangement,

means. Tye means,- b"

attesting energy virtue of which the .it mitfimifiiliy applied,

makes the control inherently more positive and etiicient than by manually operable means, and in fact, makes the ultimate result oi the operation of such a system comparable with that of the ordinary low the quency telephone circuit.

However, the sensitivity of the relays ordinarily necessary for the eflicient operation oi such systems, results in at least two functional defects.

l/Vhen the circuit is in transily occur during regular transmission, may

result in a momentary actuation of the switches to receive condition with corresponding loss of transmission. A somewhat similar result occurs in the particular form of the system in which the speech rectifier and relay are arranged so that the impressed sound energy results in a decrease in the current through the relay. Certain explosive sounds, such as the consonants p and t, have peculiar effects in such a system in that they cause a momentary increase instead of a decrease in the rectifier output (and hence relay current), and consequently a chattering of the relay contact or even an actuation of the switches to their alternative positions.

It is a further object of the invention to provide a systemotherwise as described in which these two effects are avoided.

These objects are realized, for example, in

circuits in which the switching operation afiecting the signal condition is performed by the secondary relay of an arrangement or" primary and secondary relays having a lost motion means between, whereby the movable element of the primary relay is capable of considerable movement without affecting the second relay.

The timing element provided by this fearelay is actuated so ture results in the substantial elimination of the first mentioned defect.

If the primary as to have a falling characteristic when sound waves are impressed, so that the last mentioned detect may tend to be present, this defect may also be sub stantially eliminated.

In an alternative arrangement, in which the primary relays (or if only one relay is l the relay) are actuated so as to have a re. by shot.

characteristic, the timin element is t riir'euited coil as. the re lay core This coil resists the dcencrgization of the core,'which vvould otherwise result when there is a momentary cessation or extreme decrease: in amplitude of the impressed speech waves. i

In the drawing, Fig. 1 illustrates a twoway telephone system employing the principle of the invention:

Figs. 2 and 3 illustrate a circuit which may be used alternatively to the portion of the circuit of Fig. 1 which is enclosed in dashed lines the two figures (littering only as illnst 'ating ditierent phases of ope 'ation of the circuit, and

Fig. l illustrates a still further alternative circuit which I 1y be similarly subsi tuted tor the same portion of the circuit of Fig. 1.

Referring to Fig. l. tuned antenna 1 is associated with a three-element electric discharge device 2 in su h a manner that; the combination of the elements constitutes an oscillator 0 ct well known type. (See tor example. page 360. vol. 38 No. 3 of the Proceedings of the A. l. l). 1C.) The characteristic feature of this type-0t oscillator is that the antenna, including the capacity of the aerial to ground. constiutes' its trequcncy determining circuit. The space current circuit of the oscillator may he t'aced from the 'athode, through space current source 1-3, conductor 4-, contact 5 of normally open relay switch 6, conductor 7, constant current choke coil 8, high frequency choke coil 9, to the anode of device 2.

The output current of the oscillator is modulated by moeulator M in accordance with variations of the signal current in circuit 10. The system of modulation which is used is that. usually denominated constant current modulation system. It is described in the paper (it the Proceedings of the A. I. l l. E. supra.

ln brict. the operation as "follows: Signal variations are impressed on the input circuit of the modulator and are reproduced in its output circuit in amplitied t'orm. This signal variation current flows through choke coil which is common to the space current paths ot both the oscillator and modulator. and accordingly, produces a corresponding potential drop therein, which results in a corresponding variable potential being impressed from space current source I} on the anode of the oscillator tube. These variations of potential are rci n'oduced as ampli tude variations of the generated high trequency wave. l'ligh trerpicncy choke coil 9 prevents the high 'tre ucncy currents trom lowing in the low frequency modulating circuits. Iltflv't-FYOT. the coil 9 does not have sutlicient inn'iedance to prevent the flow oi current of the modulating frequency therethrough.

The receiving circuit includes detector D and indicator ll. The detector is normally connected to coil 12, which is coupled to the antenna. through armature t and contact ll of relay 15. The relay is normally cn- -i'gi;:cd to actuate the armature to he explained later. 'jtrmaure lil oi the relay is biased upwardly spring it when relay 1?) decncrgized, the receiving circuit is opened at contact it and the transmitting circuit is closed at contact 7;. the transmitting and receiving circuits lit tad ingly being made alternately operative. Hide tone in the re civcr resulting from the locally transmitted energy the 'eby avoided.

To further insirc a complete absence of side tone. coincidental with the opening i t' the receiver circuit. or shortly thcrcattc'. the grid-cathotle circuit of the. dete tor she t circuited. is is accomplished by tl :2 contact ll. which is connected to the ca home side of the coil 12. The circuit is closed tarougi contact l7 before the il'illll .'llll .-'l tll circuit made operative and is opened alter the transmission circuit is made inoperative. so that. so Far as the litil't circuiiiug means can prevent it. the receiving circuit is at no time subjected to the hazards ot ide tone currents.

The op ration of relay 1.? is made responsive to signal variations from circuit 1 through rectifier lit and primary relay l The coil ol relay ll" energized by the space current of rectifier ll. which normally is sutlicient to hold up its armature to close a circuit through the relay 15 at contact 19.

Rectifier R functions in such a manner that impressed alternating currents. as t'rom source 10, result in a decrease ot? its space current. In order to give the tube this t': lling characteristic use made oi the l'cctitying clniracteristu: ot the input circuit in conjunction with the grid condenser 20 and leak resistance 21. i

The operation ot thc rcctiticr is similar to that ot a detecting circuit having the same elements and is well known. The rc til'ying characteristic of thc input circuit results in a pre iondcraucy ol increase over decrease of grid-tilamcnt current. Th rcsuiting increment ot' negative chargc on the grid. alter cach cyclc o l' imprcsscd potential. is trapped thereon on account oi" thc ttHl' denser il The charge on the grid tin-rci'orc tends to accumulate and continually to depress the potential of the grid iron) its normal value when no potential is impressed. the space current decreasing on rcspondinglv.

Ti hcn the space current lit-conic. sutlicic-ntly low. traction ot' -pring 32 c.\cccdthe magnetic tra tion of the coil and th circuit is closed contact lit. the ui'illui'llrrfalling back to its stop 9;). The coil oi relay l5 releases its armature 13. which l by means ice l li

lit)

is actuated upwardly by spring 16 to change the condition of the circuit as a whole from receive to transmit.

Any momentary cessation of the impressed signal, not sufficient to cause actuation of the armature of relay 18 to its circuit closing position, will not be effective to change the condition of the transmitting and receiving circuits. Further, the time constant C3.- of impedance elements 20 and 21 is made suiiiciently large so that a reasonable time must elapse, after the cessation of signals, before the current in the coil of relay 18 is sufficient to mitlate a movement of its armature away from its stop; and'so that the acceleration of its movement between stop 23 and contact 19 is small. In other words, the relay 18 is, in effect, a link between the source 10 and relay 15, the operation of this link being characterized by lost motion.

Ithas been found that the influence on the microphone of explosive sounds, such as the consonants p and t, results in an effect somewhat similar to that of a cessation of signal current. That is, it causes the space current of rectifier R to increase instead of decrease. This results from the fact that the waves corresponding to these sounds (and accordingly the potential waves impressed on rectifier R) are highly damped. Accordingly, even though by the operation of the rectifier the potential of the grid is progressively lowered by successive cycles of impressed potential, a preponderant positive impulse, such as might characterize the first half cycle of a highly damped wave might drive the grid so far positive that an appreciable time, measured by many cycles of impressed potentials, would have to elapse before the space current were again sufiiciently lowered to actuate the relay 18. The spacing of contact 19 and stop 23 is made so great' that impulses of this kind are insufficient to actuate the armature to contact 19.

Although in the description of Fig. 1 particular means for alternately rendering the transmitting and receiving circuits operative have been assumed, there are many other means for accomplishing an equivalent result. In particular, any one of the means disclosed in U. S. patent to Heising 1,488,006,

March 25, 1924, over the invention of which the present invention may be considered an improvement, may be used without requiring any material change in operation of the system or the relation of the relays and their associated circuits. Also, the falling characteristic of the space current can be obtained without the grid condenser and leak by operating over a particular portion of. the grid-potential-space-current curve.

Figs. 2 and 3 illustrate an alternative lost motion means which may be substituted for that in Fig. 1, the circuit of Fig. 2 being substituted for that portion of Fig. 1. enclosed in dashed lines. Fig. 2 illustrates the circuit when in receive condition and Fig. 3 a portion of the circuit of Fig. .2 when the circuit as a whole is in transn'iit condition. Elements having functions similar to those of 1 are similarly labeled.

In the operation of the system which includes the cir uit of Figs. 2 and 8, the circuit through relay 15 is normally broken at con tact 19, so that spring 16, instead of relay 15, norn'ially maintains the switches in receive position. Relay 15 is energized when the space current in the coil of relay 18 is decreased'sufliciently to pern'iit'spring 22 to actuate its armature to circuit closing posi-- tion, when the relay 15 will actuate the switches to transmit position. Contact 10 is resiliently held against stop 24. When the circuit is closed through this contact it is resiliently forced back a distance approximately equal to the spacing between 19 and 23 of Fig. 1 (about of an inch in a practical case). Then the space current momentarily increases, as by either of the causes described, the armature can accordingly move this distance without disturbing the condition of any of the circuits. hen contact has been made at 19, subsequent pulses of current, which would otherwise flow in the relay, are lay-passed around it through condenser 25. This tends to prevent chattering when the contact is made. This condenser is effectively disconnected when the armature of the relay is in its normal posi tion, so that it does not retard the operation when the signal is applied.

In the alternative circuit arrangement of Fig. 4, the incidence of the signal current on the rectifier results in an increase in space current on account of the rectifier characteristic of the space current circuit under vary ing grid potentials. The primary relay accordingly operates on a rising characteristic. That the rectifier may operate in this manner is apparent from the absence of a grid condenser and leak. The increase in space current is suffieient to actuate the relay 18 to circuit closing position. The subsequent operations are the same as in the system of Fig. 2.

The additional winding 26 on relay 18 has the effect of a damping coil. Its purpose is to prevent a reverse actuation of relay 18 by a momentary cessation or change in a1nplitude of the signal currents impressed on the rectifier. This winding is preferably of very low resistance, and may, for example, be a single turn of copper conductor or a copper sheath. It tends to oppose any change of flux threading therethrough by setting up an opposing flux.

The impedance elements 27 and 28 to gether constitute what is commonly called an impulse circuit. Gondenser 2'? has low impedance to the first impulse of the alter nating current component of space current, which will accordingly flow therethreugh and through the relay coil. After the relay has been a -tuated, the much smaller average current through the resistance 28 will be sutlicient to hold the relay in operated position. By the use of this a rangement, since the current through the coil of the relay "for the steady state will be less 'llflll that corresponding to the initial impulse, and since it is a steady current that determines the necessary ljiiasing pull of spring 22, a smaller biasing spring can be used with consequent increase in llevibilit and sensitivity. From another point of view, the use of the resistance makes possible the use of a space current source having a large potential without unduly increasing the relay current during the steady state. On account of the condenser 27 the whole oil this large potential is momentarily available to actuate the relay wh *n the lirst impulse ot current impressed on the rectitier. A somewhat similar use ol an impulse circuit is disclosed in Fig. 12 ot' ll. S. patent to Deardoril rlo. l,i t :l-,1l;(l8, granted November 20, 192 5.

Obviously, the anions features disclosed, iespectively, as applied to individual circuits can be used in others ot the circuits, or a combination of features disclosed in separate circuits may be used in a single circuit. For example, the lost motion contact member of Fig. 2 can be used in the system of Fig. -l by making contact 19 resilient; the impulse circuit of Fig. rcan be applied to a circuit having the lost motion means (it either Fig. 1 or Fig. 2; the. system of Fig. l -an be caus d to operate on a tailing char; cteristic, the contacts being rearranged accordingly in a manner taught by Fig. 2; etc.

hat is claimed is:

'1. A station of a two-way signal svstem comprising means for transmitting a signal, means for receiving a signal, and relay-including means actuated in response to the initiation and cessation of said signal transmission to respectively render said station (1pc 'ative tor signal transmission and reception. said means including circuit closing means whereby said relay operates to initiate the change in condition ol said stas tion a predetermined time after the cessation ol the previous condition of signal operation.

2. i. station of a two-way signal system comprising means for transmitting a signa wave. means For receiving a signal wave, and signal actuated means for rendering said station exclusively operative for transmission during signal transmission, said means comprising mechanical lostanotion means whereby said station becomes inoperative for transmitting a predetermined rpcrative. a

said relay, a normally energized relay For maintaining closer in circuit closing position, biasing ncans tor ach of said circuit closers. means esponsive to signal transmission for desaid last mentioned circuit 'zing v said said last mentioned relay wherelast mentioned circuit closer is iiased to open circuit condition, and a stop o limit the traverse ol said last mentioned ircuit closer between its normally open and normally closed positions.

l-. A sound controlled relay system coinl l t electrical discharge device for generating fl "frequency waves, an electrical dis :arge device for modulating said high "lie nency waves in accordance with said modlating current, a space current circuit including a switch for at least one of said devices, a normally operative receiving circuit including an electri-al discharge device, circuit means including a switch for shortcircuiting at least a portion of said receiving device. a biased normally encrgized relay for maintaining each ol said switches in ntni-circuit closing position, an electrical discharge device crnitaining a cathode, an anode. and an impedance control element. an input circuit in energy transter relation to said modulating current source and to said cathode and co ni'ol element. and including a capacity ele ment in series with said control element, and a high impedance induction path between said cathode and control element. a space current circuit between said cathode. and said anode. and including a relay. a switch in circuit with said first mentioned relay and in energy transfer relation to the last mentioned relay. and a stop to limit the traverse ol said last mentioned switch bctween its actuated and non-actuated positions.

A sound controlled relay system comprising an antenna, means tor producing and radiating from said antenna a signal modulated high frequency wave including an electrical discharge device having switch-contaiuing space current circuit. circuit including an electrical discharge detector for receiving signal modulated high ltlt) frequency waves in energy transfer relation to said antenna, a switch connecting said receiving circuit with said antenna, a switchcontaining short-circuiting means for said detector, biasing means for each of said switches, a normally energized relay, said switches and biasing means being so arranged that, when said relay is energized, the second mentioned switch is in circuit closing position and the first and third mentioned switches are in open circuit position, a circuit closer in circuit with said relay,

a normally energized relay for maintaining said circuit closer in actuated position, means responsive to signal transmission to deenergize said last mentioned relay, whereby said switches and circuit closer are biased to their respective alternative positions, and a stop to determine the open position of said circuit closer.

In witness whereof, I hereunto subscribe my name this 31st day of January A. D.,

JOHN c. GABRIEL. 

